1. Field of the Invention
The present invention relates to an identification apparatus for identifying an individual using vital information, and, more particularly, the present invention relates to a finger identification apparatus that utilizes a hemal pattern of a finger and methods therefor.
2. Description of the Background
An individual identification technology is expected to enable the safe management of property and/or information. In particular, living body (personal) identification technologies that utilize parts of a human body as a key are beginning to attract attention. One reason for this is because a living body identification technology has a reduced chance for an illegal access to property or information resulting in a loss or robbery as compared to conventional technologies for managing property and information using a password or a key. Living body identification technologies include various techniques based on a fingerprint, a face, an iris, or a hemal pattern of a hand or a finger.
Among these techniques that are currently under study, the identification technique utilizing a hemal pattern of a finger is advantageous in that: (1) the technique reduces a user's reluctance to undergo identification because the technique is not associated with crime (unlike a technique utilizing a fingerprint); (2) the technique does not require direct irradiation of light into an eye (unlike a technique utilizing an iris); and (3) the technique reduces the possibility of forgery because it reads an internal feature of a living body instead of a superficial feature thereof.
The process for identifying an entity utilizing a hemal pattern of a finger will be described below. Initially, a light source for radiating near-infrared light is made available, and a camera is placed facing the light source so that the camera can pick up only light emanating from the light source image. The camera is provided with an optical filter that passes light with wavelengths which fall within the near-infrared band. For identification, a finger is interposed between the camera and light source in order to image the finger. Since hematic components absorb near-infrared light efficiently, the digital blood vessels do not transmit light and are therefore visualized dark (i.e., appear dark in the resultant image). The resultant image of a hemal pattern is then compared with an image of a registered pattern, whereby individual identification may be performed.
In order to correctly determine a correspondence between a hemal pattern and a registered pattern, an image must be produced under the same conditions for imaging between registration and identification. For example, if a finger is turned, a visualized hemal pattern is quite different from a registered pattern. As long as a finger is displaced or turned with its surface to be imaged held unchanged, an image of a hemal pattern produced during identification can be corrected readily through image processing. However, if a finger is so turned that the surface thereof is reversed from the dorsal side to the ventral side or vice versa, an image of a hemal pattern cannot easily be corrected because some blood vessels are unknown.
For example, an identification apparatus that utilizes the hemal pattern of the palm of a hand directs a user to hold a guide bar with his/her four fingers for positioning. The position of the palm of an individual's hand to be imaged is thus made invariable. However, as far as the digital blood vessels are concerned, if a user holds the bar or the like with his/her fingers, or, if a user stresses his/her fingers in some way, the digital blood vessels are compressed (as described above). Consequently, part of a hemal pattern may be missing or obscured. Another conceivable method is such that a guide rail or the like is included and a user is asked to place his/her fingers at a specified position on the guide rail. However, this method requires a user to learn how to place his/her fingers correctly. This means that not everybody can easily use the apparatus.
Moreover, a visualized hemal pattern varies depending on the posture of a finger inserted in an identification apparatus. For example, when a finger extended excessively with force has the blood vessels thereof compressed due to the epidermal stress, part of a hemal pattern may be missing. When extraneous light illuminating the entire identification apparatus changes, the brightness or contrast of a produced image varies. This may adversely affect precision in identification. Specifically, near-infrared light contained in ordinary sunlight or illumination light may adversely affect visualization of a hemal pattern.